Bound- and bi-excitons in ZnCdSe/ZnSe multiple quantum wells

Using a set of high-quality MBE grown samples, a systematic study of bi- and bound-excitons in wide-gap II-VI quantum wells is carried out for the first time. The assignment of low-energy photoluminescence lines to these complexes is accomplished by their characteristic polarization properties in a magnetic field. The binding energy of the bi-exciton increases with growing band offset. A similar tendency is found for the bound-exciton, however, with generally smaller binding energies. The larger values found for the bi-exciton are attributed to localization on alloy fluctuations which is qualitatively confirmed by density functional calculations. Time-resolved photoluminescence is used to study the formation and decay kinetics of bi-excitons.